DEUTERIUM-EXCHANGE STUDIES OF THE INTERFACIAL RATE OF REACTION OF WATER-VAPOR WITH SILICA-SATURATED IRON SILICATE MELTS

Measurements have been made of the rate of dissociation of H2O on silica-saturated iron silicate melts at 1300 °C and 1400 °C by the HDO-H2 deuterium exchange technique. The general rate equations for the technique are developed, and the available information on the associated isotope equilibria is briefly reviewed. The rate is deduced to be first order with respect to the pressure of water vapor, and the apparent first-order rate constant is found to be essentially inversely proportional to the activity of oxygen in the melt over the range studied;i.e., pH 2O/ pH2 - 0.9 to 18 at 1400 °C. Comparison with the rates deduced by Sasaki and Belton from measurements of the steady-state oxygen activity of the melts in flowing H2O-CO mixtures at 1250 °C leads to the conclusion that interfacial rates of oxidation (or reduction) of the melts in H2O-H2 atmospheres are given by the rate law v = k1(pH2O(a′o) -pH 2) over the range of conditions covered by the two sets of experiments. The term a'o is the oxygen activity of the melt, defined as the equilibrium pH 2O/pH2 ratio, and k1, in units of mol cm-2s-2 atm-1, is given by the expression: log k1 = -6700/T - 0.08 to within a factor of about 2 over the temperature range of 1250 °C to 1400 °C. © 1990 The Minerals, Metals & Material Society.